Real-time inverse kinematics for the upper limb: a model-based algorithm using segment orientations

Bence J Borbély,Péter Szolgay

doi:10.1186/s12938-016-0291-x

Bence J Borbély, Péter Szolgay

Open Access

https://doi.org/10.1186/s12938-016-0291-x

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Abstract

BackgroundModel based analysis of human upper limb movements has key importance in understanding the motor control processes of our nervous system. Various simulation software packages have been developed over the years to perform model based analysis. These packages provide computationally intensive—and therefore off-line—solutions to calculate the anatomical joint angles from motion captured raw measurement data (also referred as inverse kinematics). In addition, recent developments in inertial motion sensing technology show that it may replace large, immobile and expensive optical systems with small, mobile and cheaper solutions in cases when a laboratory-free measurement setup is needed. The objective of the presented work is to extend the workflow of measurement and analysis of human arm movements with an algorithm that allows accurate and real-time estimation of anatomical joint angles for a widely used OpenSim upper limb kinematic model when inertial sensors are used for movement recording.MethodsThe internal structure of the selected upper limb model is analyzed and used as the underlying platform for the development of the proposed algorithm. Based on this structure, a prototype marker set is constructed that facilitates the reconstruction of model-based joint angles using orientation data directly available from inertial measurement systems. The mathematical formulation of the reconstruction algorithm is presented along with the validation of the algorithm on various platforms, including embedded environments.ResultsExecution performance tables of the proposed algorithm show significant improvement on all tested platforms. Compared to OpenSim’s Inverse Kinematics tool 50–15,000x speedup is achieved while maintaining numerical accuracy.ConclusionsThe proposed algorithm is capable of real-time reconstruction of standardized anatomical joint angles even in embedded environments, establishing a new way for complex applications to take advantage of accurate and fast model-based inverse kinematics calculations.

Highlights

Model based analysis of human upper limb movements has key importance in understanding the motor control processes of our nervous system
Purpose of the study The main goal of this study is to extend the measurement and analysis workflow of human arm movements with a method that allows accurate and real-time calculation of anatomical joint angles for a widely used upper limb model in cases when inertial sensors are used for movement recording
The results show that considering the mean of all valid trials (59 for OpenSim, 100 for all others), all platforms performed reasonably well producing errors below 3° for all joint coordinates

Summary

Introduction

Model based analysis of human upper limb movements has key importance in understanding the motor control processes of our nervous system. And Szolgay BioMed Eng OnLine (2017) 16:21 research activity in movement rehabilitation [1,2,3,4], performance analysis of athletes [5] and general understanding of the motor system [6,7,8,9] during the last decades by making movement pattern comparison possible This advancement was further accelerated by model-based analysis approaches that enabled explicit characterization of the studied movement patterns [10,11,12,13,14,15]. Having the markers in place, measurements have to be performed in a specialized laboratory environment where locations and orientations of the sensor elements (i.e. cameras or microphones) are known and invariant (at least across trials) This means that even the spatial positions of the markers can be determined with good accuracy—especially with optical systems—the possible range of motion will always be constrained by the actual measurement volume covered by the sensors of the system. This property is not an issue for many movement analysis scenarios, there are cases when a measurement method allowing unconstrained free space movement would be more beneficial (e.g. various outdoor activities or ergonomic assessment of work environments, to name a few)

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